1. Field of the Invention
The present invention relates to a method and apparatus for applying to the skin, in a controlled manner, a radio frequency generated plasma in order to heat and selectively damage thin superficial layers of the skin, thereby inducing a renewal process of the epidermis.
2. Description of the Related Art
It is well known in the skin treatment art that in order to renew the epidermis layer, induced damage of the skin is required. One such method uses laser radiation that is incident on the skin and that generates several effects on the skin, depending on the wavelength of the laser radiation, the pulse duration of the laser energy applied to the skin, and the radiation energy provided to the skin.
The most commonly used method is CO2 laser radiation for generating a superficial heating of the skin. When laser light reaches the skin, its intensity decreases exponentially as it progresses down into lower layers of the skin. This means that the thermal energy that is delivered is higher in the first layer and decreases exponentially as its progresses down to lower layers of the skin. Moreover, the first corneum stratus of the skin has a higher absorption than other layers. Such an energy profile is not suitable for a uniform heating of a volume of skin due to the fact that in the superficial (upper) layers, the reached temperature is too high and in the lower layers the reached temperature is not high enough to trigger the desired skin treatment process.
The present invention utilizes a method and apparatus of heating a superficial portion of skin using a combined action of radio frequency and a plasma generated by the same radio frequency.
Two principles are used in the present invention. First, radio frequency currents are localized in the external layer of the skin due to the skin effect, and thus the heating is localized in a thin (upper) layer of skin.
It is well known that an alternating voltage applied to a conductor generates a current on the external layer of the conductor and the depth depends on the frequency and the resistance of the conductor (so-called skin effect).
Second, the plasma generated at the contact of the skin, due to the radio frequency and a high vacuum generated by a suitable pump, is composed of high energy gas ions that strike the surface of the skin, thereby generating heat in the superficial layer of the skin.
The interaction with the skin has some similarities to the interaction described in the patent application entitled xe2x80x9cMethod and Apparatus For Skin Brown Spot Removalxe2x80x9d, patent application Ser. No. 09/361,407, which is incorporated in its entirety herein by reference.
One advantage of such an approach is by not having electrodes in contact with the skin, a more even distribution of the radio frequency current in the skin is achieved. Also, there is achieved a combined action from the striking gas ions and a more accurate control of the power applied to the skin surface, due to the higher impedance of the plasma that controls the current independently from the electrical conductivity value of the skin.
The present invention relates to an apparatus and a method for skin resurfacing treatment, which provides induced thermal damage of the skin by radio frequency heating and by ion bombardment of the skin.
This dual effect may be achieved by using a pulsed radio frequency generator connected to a probe for coupling to the skin. The probe is preferably made of a non-conductive material (such as glass or plastic), and enables the application of a high vacuum to the skin surface (e.g., 5-10 millibars) over a predetermined (e.g., round) portion of the skin, by using a non-conductive pipe connected to a vacuum pump. At a suitable distance (around 10 millimeters) from the surface of the skin, an electrode (that is housed within the probe) is used to generate a radio frequency field between the electrode itself and the surface of the skin. After reaching a sufficient vacuum (e.g., 5-10 millibars of atmospheric pressure), a high voltage radio frequency electric field is applied between the electrode and the surface of the skin, due to a radio frequency pulse applied to the electrode. Such a radio frequency field triggers a glow discharge inside the probe between the electrode and the skin. A radio frequency current, due to the low impedance of the glow discharge, flows evenly on the surface of the skin, and, due to the skin effect, is limited to the glow discharge area in a depth of about 300 microns. In the surrounding tissues, the current density decreases by the square of the distance from the area covered by the glow discharge within a depth of 300 microns. Moreover, the high energy ions of the glow discharge strike the surface of the skin, thereby providing a plasma skin resurfacing that can be used to remove spider veins, skin brown spots, or port wine stains, for example.
The present invention provides a controlled heating of a selected portion of the skin to a depth of about 300 microns. As a result, it is possible to reach a desired temperature of 70 degrees C. or more, which triggers controlled damage to the skin cells to achieve. a desired effect. The temperature reached in the described volume of the skin depends primarily on the selected pulse length and the power of the radio frequency generator. Preferably, a temperature reached in the described volume of the skin is a temperature in the range of from 75 degrees C. to 95 degrees C.
To achieve a substantially uniform heating of a volume of the skin, a method according to the invention includes:
1) Application of a probe to the skin, where the probe is held against an open area on the skin of about one square centimeter, where the probe includes an electrode at a distance of 10 millimeters (plus or minus a few millimeters) from the skin surface, and where a vacuum suction pipe is connected to the probe.
2) Generation of a high vacuum inside the probe and at the surface of the skin by connection of the probe to a high vacuum pump, by way of the vacuum suction pipe.
3) Application of high voltage at a frequency of 21 MHz in the probe between the electrode and the skin, by way of a pulsed radio frequency generator connected to the probe by way of a conductive cable.
4) Generation of a glow discharge for a time less than 1 second sustained by a power less than 500 W.